#include<bits/stdc++.h>
using namespace std;
#define pi 3.1415926535897
bool searchPie(double x);
double pie[100000];
int n,f;
int main()
{
	double mx=-1.0*0x3f3f3f3f;
	cin>>n>>f;
	for(int i=1;i<=n;i++)
	{
		cin>>pie[i];
		pie[i]=pi*pie[i]*pie[i];
		if(mx<pie[i])
			mx=pie[i];
	}
	double l=0,r=mx,res;
	while(l<=r)
	{
		double mid=(l+r)/2;
		if(searchPie(mid))
		{
			l=mid+0.00001;
			res=mid;
		}
		else
			r=mid-0.00001;
	}
	printf("%.3f",res);
    return 0;
}
bool searchPie(double x)
{
	int num=0;
	for(int i=1;i<=n;i++)
		num+=pie[i]/x;
	if(num>=f+1)
		return true;
	else
		return false;
}
